1. Field of the Invention
The present invention relates to a camera system that attaches an intermediate accessory between a camera and an exchange lens.
2. Description of the Related Art
In the camera system including a camera and an exchange lens, optical information peculiar to an exchange lens, such as information of a focal length, a stop, focus sensitivity, and a focus correcting amount) is communicated to the camera. When possessing the optical information peculiar to the exchange lens, the camera can provide appropriate autofocus (“AF”) and auto-exposure (“AE”) in combination with that exchange lens.
One of such camera systems may enable an intermediate accessory, such as an extender, to be attached between the camera and the exchange lens. When the intermediate accessory is attached, the optical information peculiar to the intermediate accessory as well as the optical information of the exchange lens needs to be considered in order to provide proper AF, AE, etc., in the camera. Thus, when an intermediate accessory is attached, the camera or exchange lens detects the intermediate accessory and the optical information of the exchange lens needs to be corrected based on optical information of the intermediate accessory.
However, when a new intermediate accessory with a new design is combined with an old camera and an old exchange lens each of which has an old design or function, the old camera and the old exchange lens have no optical information of the new intermediate accessory and thus cannot provide the above correction processing of the optical information.
As one solution for this problem, an intermediate accessory disclosed in Japanese Patent Laid-Open No. (“JP”) 63-199335 includes an internal CPU and the accessory CPU converts or writes down optical information transmitted from the exchange lens to the camera, into data that reflects influence of optical information of the intermediate accessory. In addition, the intermediate accessory disclosed in JP 2002-341424 corrects optical information of an exchange lens and transmits it to the camera when the combined camera and exchange lens are old types.
When a new camera and a new exchange lens are combined with each other and the combination can provide correction processing to the optical information of the exchange lens based on the optical information of the intermediate accessory, it is unnecessary for the intermediate accessory to perform the correction processing of the optical information by itself. Therefore, the intermediate accessory if attached to the new camera and the new exchange lens may transfer to an operational state that prohibits the correction processing in order to save the (useless) power consumption for the correction processing.
At that time, if the power supply to the intermediate accessory is interrupted to stop its operation, the intermediate accessory does not respond to a new camera's request for information necessary for the operation of the camera, such as identification information of the intermediate accessory.
In addition, if a new camera communicates with a new exchange lens with a protocol which the intermediate accessory cannot normally recognize before the intermediate accessory detects the new camera and the new lens, the intermediate accessory may work improperly and consequently the entire camera system is likely to malfunction.